Galaxy Zoo Talk

"Green cloud merger"

  • GBendt by GBendt

    On he first glance, this looks like a normal merger of two spiral galaxies, their shapes heavily disturbed by the effect of tidal forces. But three aspects are unusual.

    1. Firstly, one galaxy features a ring of young blueish stars around
      its core, Such rings can appear as a result of a central collision
      of two galaxies, where one galaxy travels through the center of the
      disk of the other.
    2. Further, the upper area of the galaxy seems to be covered by some
      dust, which also covers the tidal tail of the second galaxy which
      seems to have no core. Such vast unstructured dust clouds are very
      unusual. This might meean that the dust cloud is much closer to us
      than it looks like on the first glance.
    3. And finally, there is some vast greenish cloud, almost as large as the
      radius of the ring of stars of the first galaxy. If the cloud is associated
      with the galaxy, the energy source which causes the emission of the
      greenish light must be enormous in size and output. But I dont´t see
      such a source. Where is it, and what is it? Does anyone have an
      idea?

    Posted

  • Budgieye by Budgieye moderator

    1. Can someone who understands the extra processing that the AHZ... images help here?
      Is the blue ring an artifact or is it real?

    2. The "dark dust" is probably an imaging artifact. These images are heavily processed to remove cosmic ray hits. You can see dark loops in the image where objects were lassoed.

    3. green cloud is an artifact, the green colour is spread in the direction of the line of pixels.

    ![AHZ..] (http://www.galaxyzoo.org.s3.amazonaws.com/subjects/standard/1237678889056272553.jpg)
    dr8

    image in Examine and dr8 http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237678889056272553
    outside dr7

    Posted

  • planetaryscience by planetaryscience

    Budgieye, I'm not and expert on how these are processed, but having experience with galactic morphology and shapes, I can confirm that the 'ring' is real. Essentially what's going on is that two galaxies are merging. They have already passed through each other once, and the ring you see is the result of this pass-through, but the disturbed part you see is what remains of the smaller galaxy that passed through the larger one. The green line is an artifact.

    Posted

  • Budgieye by Budgieye moderator in response to planetaryscience's comment.

    Sounds very exciting, but we should gather more facts before putting together a merging model like that.

    Posted

  • Capella05 by Capella05 moderator

    Having discounted the green line as an artifact, what is to stop this from being a overlap?

    Posted

  • JeanTate by JeanTate

    Here's the SDSS DR8 version of this galaxy (but see below):

    enter image description here

    This is, obviously, zoomed in a lot. I did this deliberately, to illustrate the fact that features, broadly defined, become washed out when you increase the magnification.

    Which raises the question: how can you tell whether a fine (small-scale) feature is likely to be real or not?

    The answer is tied to the smallest 'thing' the SDSS camera can 'see'. And that in turn is tied to something called the 'point spread function' (PSF), or 'seeing' as it is known to amateur astronomers*.

    This image is a composite of three separate images, one each in the g, r, and i SDSS bands/filters. Each has its own PSF, and if the PSFs are significantly different, you will see color artifacts in the image, especially given the extreme image processing that has taken place to produce this particular image.

    I haven't checked this particular image, but typically r-band SDSS images have PSFs with a FWHM (full-width at half-maximum; a measure of 'size') of ~1.4". In g-band images the PSF is generally bigger; the i-band one ~the same.

    In this object, which features are clearly bigger than ~1.5"?

    *yes, technically the two are not the same; for the purposes of this post, let's treat it as a 'lie to children'WP

    Posted

  • Budgieye by Budgieye moderator

    AHZ... images for galaxy have been treated differently to bring out features, but I can't find the reference, and perhaps it had been referring to the infrared data. Also, are the images still a bit blurry after being sent over the internet, to save bandwidth?

    Posted